Line a 9 inch square baking pan with foil, grease the foil set aside. In a large bowl, combine the first five ingredients. Cut in butter, stir in the egg yolk, vanilla and walnuts. Press into bottom of prepared pan bake at 325 for 15 minutes. Remove and let set until next step is done.
In a small bowl, beat cream cheese, sugar until smooth. Beat in the sour cream, flour, orange peel and salt. Beat in the egg, egg white and vanilla on low speed until combined. Pour over warm crust and bake for 25 minutes or until center is set. Cool on wire rack at least 1 hour. Refrigerate overnight. Cut into squares after lifting out of the pan and removing the foil.